Abundances in globular cluster red giants. I - M3 and M13

A detailed abundance analysis of five red giants in M13 and three in M3 has been performed using line-blanketed model atmospheres. Abundances have been determined for over 20 elements in each star. The mean Fe deficiency is -1.6 dex for M13 and -1.8 dex for M3, while M3 is marginally more metal-rich in Mg and Si than M13. Although all elements (with the probable exception of Na) have the same abundance in each of the five M13 stars, considerable scatter exists for Na and Ca and perhaps other elements in the M3 stars. Fe and elements heavier than Fe have the same abundance in each of the three M3 red giants. It appears impossible to explain all the deduced scatter in M3 either by errors in the analysis or by convective mixing. Therefore, the primordial gas in M3 was not chemically homogeneous during the time interval when star formation of the currently observed M3 red giants took place.